The Detroit News has put together a rundown of all the little tweaks automakers are applying, as quickly as possible, to help current models achieve better fuel economy. Since a wholesale re-engineering of every vehicle is impossible, manufacturers are switching to low-rolling-resistance tires, re-gearing transmissions, moving from belt-driven accessories to electric, and so on. Each change accounts for only a tiny improvement on its own, but added up, the results can make a big difference.For instance, the wrapper on the 2009 Chevrolet Cobalt XFE is little changed over the 2008 Cobalt, but underhood the engineers tweaked the intake and exhaust valve lift duration, swapped the transmission gear ratios for lower operating revs, and put on some low-rolling-resistance tires. The result: one more mile per gallon over last year's model, up to 37 MPG. It may seem like a lot of work for that much payoff, but the competitive marketplace is a cut-throat kind of place, and nobody is standing still in the race for fuel economy. [DetNews]